The present invention relates to control apparatus for regulation of the deceleration of a moving object just prior to its total stop during a time which can vary but over a constant distance whatever the inertia, the acceleration and the initial velocity of the moving object.
The present invention applies more particularly but not exclusively to elevators, invalid carriers, load carriers and similar apparatus which during their arrival at a predetermined distance from the platform, corresponding to the ascending or descending control being carried out, causes the emission of an order for stopping at the selected level and thus over a given distance.
To obtain this stop the apparatus must in a first period of time reduce the velocity and then in a second period of time apply a stopping brake.
To provide for the comfort of the users of the elevator, and of the sick and/or persons to undergo a surgical operation and being moved in a lift for the ill, and also so as not to brake or upset objects being transported in such apparatus, it is important that these moving elements have a regular deceleration and as slowly as possible, but sufficient so that the actuation of the stopping brake does not cause an abrupt stop. To this end, the stopping brake should only be applied at the end of displacement of the elevator, that is, when its speed is practically zero. However, this stop must nevertheless occur exactly at the level of the platform for the comfort of the users and to facilitate access of wheeled vehicles or the handling of objects in the elevator.
Certain elevators utilize only a single speed motor and a brake which is progressively actuated to slow the elevator and then stop it. The action of braking is against the inertia and the action of the motor from the beginning of the deceleration heats the structure and rapidly deteriorates the brake linings without providing a regularity of the deceleration or the stop without an abrupt change.
To decrease the time of action of the brake, other elevators utilize two speed motors which receive two distinct signals to stop them. The first signal controls the movement to low speed and the other causes the action of the brake. Unfortunately, there is a jolt caused by the change of speed in the movement of the lift and the lift can still have a rather high speed particularly if the lift is in descent and loaded and because of this the stopping is abrupt. Further, such a motor having double coils is quite costly.
In prestigious installations where the high cost of the apparatus is not a consideration, variable speed motors are used controlled by complex regulators which provice a quite regular deceleration of the elevator in comparison with the actual decrease of the speed as compared to the desired decrease as a function of time beginning with the start of the decrease of velocity and acting on the braking force and/or the current feeding the motor as soon as the difference between the actual decrease and the desired decrease passes a predetermined value.
If there is no difference between the two values, the stop would occur in the given time and over the available distance.
However, these differences occur which are inevitable and caused primarily by the differences of weight in the elevator. The stopping distance is varied and the result is a stop out of level with the platform, in accordance with the sense of the difference with an abrupt stop before the normal end of deceleration or the motor must be reenergized to maintain speed to reach the platform which greatly increases the time of response to the orders of the users.